This invention relates to optically active transparent composites and in particular to composites used for the shielding of infrared heat energy and UV radiation.
A conventional heat shielding transparent composite may comprise a very thin layer of a reflective metal such as silver or aluminum which is deposited on a transparent substrate by vacuum deposition, or sputtering techniques. However if such composites are utilized for the windows of buildings or vehicles the film thickness must be extremely thin to avoid high levels of reflectance and maintain a high level of visible light transmission (VLT) of at least 70%. Metallic layers are also prone to corrosion problems.
In order to avoid the above problems some film composites are coated with anti-reflective layers.
It is known that nanoparticles of various inorganic metal compounds, in particular oxides, can be dispersed within a resin binder to form coatings that reflect or absorb particular wavelength bands of infrared energy and allow high levels of transmission of visible light. In particular U.S. Pat. No. 5,807,511 discloses that antimony doped tin oxide (ATO) has a very low transmission to infrared light having a wavelength exceeding 1400 nm, and from U.S. Pat. No. 5,518,810 it is known that coatings containing tin doped indium oxide (ITO) particles also substantially block infrared light with having wavelength above 1000 nm, but the crystal structure of ITO can be modified to block light having wavelengths of down to 700-900 nm. U.S. Pat. No. 6,060,154 discloses the use of fine particles of ruthenium oxide, tantalum nitride, titanium nitride, titanium silicide, molybdenum silicide and lanthanum boride to block light in the near infrared range. It also discloses the use of a plurality of different films each selectively transmitting light.
EP-A-739272 discloses a typical transparent polymeric film having UV absorbing properties.
EP-A-1008564 discloses the use of an infrared blocking coating composition which contains both ATO or ITO, and metal hexaboride. The ATO or ITO blocks the higher wavelengths of infrared light and the hexaboride particles block the lower wavelengths of light. The coating may be applied to polymeric film substrates.
The present invention seeks to provide a thin transparent film layer having visible light transmission which shields against infrared light over a wide wave band and which is easy and economic to manufacture commercially.
According to the present invention there is provided an optically active film composite including a layer of resin binder having a thickness of less than 6 microns and a pencil hardness of at least 2H, preferably 3H, and including nanoparticles of at least one metallic compound absorbing light having a wavelength in the range of 1000-2500 nm, and nanoparticles of a second metallic compound being an inorganic compound and absorbing light having a wavelength in the range of 700-1100 nm. Preferably the composite has a VLT of at least 50% and a % TSER of at least 35%, and more preferably has a VLT of at least 70%. For a composite having VLT in the range 50-60% the t TSER may be between 50-65%.
Pencil hardness is measured according to ASTM D3363-92a.
VLT is visible light transmission calculated using CIE Standard Observer (CIE 1924 1931) and D65 Daylight.
The % TSER is percentage total solar energy rejection which is calculated from optical and heat rejection properties of coated film measured on a Varian Analytical Cary 5 spectrophotometer in accordance with ASTM E903-82, the absorption and transmission data being analyzed using parameters described by Perry Moon in the Journal of the Franklin Institute Vol. 230 pp 583-618 (1940).
Nanoparticles are particles having an average particle diameter 200 nm or less, and preferably less than 100 nm.
Preferably, said one metallic compound is Antimony Tin Oxide (ATO), Indium Tin Oxide (ITO), or Tin Oxide.
Preferably said one metallic compound is ATO and the layer contains 30-60% by weight of ATO, preferably 50-60% by weight of ATO.
Said second compounds may be modified ITO as is described in U.S. Pat. No. 5,807,511 and/or at least one of a metal hexaboride taken from lanthanum series of the periodic table, the preferred hexaborides are La, Ce, Pr, Nd, Gb, Sm, and Eu with La being the most preferred option.
Said layer contains a maximum of 3% by weight of said second metallic compound, preferably less than 2%, and more preferably between 0.5%-2%. In a preferred embodiment, the weight ratio of said second compound particles to the sum of said second compound particles and said first compound particles ((Weight of 2nd compound particles/Weight of first compound particles +second compound particles) *100%) is 1.08%-3.53%, as illustrated by the data in Table 5.
The binder may be a thermoplastic resin such as an acrylic resin, a thermosetting resin such as an epoxy resin, an electron beam curing resin, or preferably a uv curable resin which may be an acrylate resin of the type disclosed in U.S. Pat. No. 4,557,980, or preferably a urethane acrylate resin.
Said layer is electrically non-conductive which makes it particularly useful for applications relating to automobile windshields or rear windows especially those containing radio aerials.
Said layer may be coated to a transparent polymeric film substrate, preferably a polyester film which is more preferably polyethyleneterephthalate (PET) film. The infrared blocking layer forms a hardcoat for the film substrate which is particularly advantageous and may cut out a further processing step during composite film manufacture. The PET film may be coated with an adhesive for fixing the film composite to for example an existing window of a building or automobile. The PET film and/or adhesive may include at least one uv radiation absorbing material to block out substantially all uv radiation to less than 1% weighted UV transmission.
Weighted UV transmission is derived from measurements made in accordance with ASTM E-424 and as modified by the Association of Industrial Metallisers, Coaters and Laminators (AIMCAL).
Such composites have low visible reflectivity of less than 10% and have excellent weatherability with no loss of absorption properties, and holding color, after 1500 hours in a Weatherometer.
The composite may further include at least one glass sheet, which may be laminated or a single sheet, to which the coated film is adhered, preferably using a pressure sensitive adhesive The coated film may be sandwiched between two glass sheets
In some environments a % VLT of less than 50% may be acceptable combined with a higher heat/IR rejection properties. According to another aspect of the invention there is provided an optically active film composite including a polymeric film substrate coated with a layer of resin having a thickness of between less than 6 microns, the resin including nanoparticles of ATO, and nanoparticles of a second metallic compound being an inorganic compound and absorbing light having a wavelength in the range of 700-1100 nm, the composite having a VLT of greater than 50% and a % transmission of light at 940 nm wavelength of no more than 10%.
A further aspect of the invention provides an optically active film composite including a transparent substrate coated with a layer of resin having a thickness of less than 6 microns and containing nanoparticles of ATO, and nanoparticles of a second metallic compound being an inorganic compound and absorbing light having a wavelength in the range of 700-1100 nm, with a second transparent substrate located on said layer so that said layer is sandwiched between the two substrates.
Said substrates may be PET film or glass.
With the resin layer located within the composite the optical properties of the resin layer are stabilized and have improved weatherability.
Also according to the invention there is provided a method of manufacture of an infrared energy shielding film hard coat, wherein a dispersion of nanoparticles of at least one metal compound absorbing light in the waveband 1000-2500 nm in a solution of a polymeric resin, is mixed with a second dispersion of nanoparticles of a second metallic compound absorbing light in the waveband 700-1100 nm in a liquid compatible with said solution, the liquid mixture being coated as a thin layer on a substrate and dried to form said hard coat.
The substrate is preferably PET film whose surface may be treated for adhesion of the layer. The coated film is dried by passing under UV lamps having a rating of at least 300 watts per inch at a linear speed of at least 50 ft per min.
The liquid mixture may be applied to the film by any suitable method for example roller coating in particular using gravure printing techniques, slot die coating, bar and blade coating.